Genetics and Disease Practice Questions

Q: Which of the following statements about Hemochromatosis is true?

Inherited as an autosomal recessive disorder. Explanation: Hereditary Hemochromatosis (HH) is a disorder of iron metabolism characterized by increased intestinal iron absorption, leading to iron deposition in various organs (liver, heart, pancreas, and joints). 1. Why Option D is Correct: The most common form of Hemochromatosis (Type 1) is caused by mutations in the HFE gene (most commonly C282Y) located on Chromosome 6 [2]. It is inherited as an autosomal recessive disorder. This means an individual must inherit two mutated alleles to be at risk for the phenotypic expression of the disease [2]. Both the C282Y and the H63D mutations can be identified by genetic testing, which is now in routine clinical use [1]. 2. Why the Other Options are Incorrect: * Option A: While phlebotomy is the treatment of choice and can normalize life expectancy if started early, it is not "curative" in a genetic sense [1]. The underlying genetic defect remains, and the patient requires lifelong monitoring and maintenance therapy [1]. * Option B: Although the gene frequency is equal in both sexes, the disease is more common in males (approx. 5:1 to 10:1 ratio). Females are "physiologically protected" due to iron loss during menstruation and pregnancy, delaying clinical presentation. * Option C: Hemochromatosis is a classic example of incomplete penetrance. Many individuals homozygous for the C282Y mutation never develop clinical symptoms or significant iron overload [1]. Clinical Pearls for NEET-PG: * Classic Triad (Bronze Diabetes): Cirrhosis, Diabetes Mellitus, and Skin Hyperpigmentation [2]. * Early Sign: Arthropathy (specifically involving the 2nd and 3rd metacarpophalangeal joints). * Diagnosis: Best initial test is Transferrin Saturation (>45%); Gold standard for diagnosis is HFE Gene Analysis [1]. * MRI: Used to quantify hepatic iron (shows low signal intensity on T2-weighted images) [1]. * Most common cause of death: Hepatocellular Carcinoma (HCC) [2].

Q: Which one of the following neurological conditions is not inherited in an autosomal dominant pattern?

Friedreich's ataxia. **Explanation:** The core concept tested here is the mode of inheritance for common genetic syndromes encountered in neurology and medicine. **1. Why Friedreich’s Ataxia is the correct answer:** Friedreich’s ataxia (FA) is an **Autosomal Recessive (AR)** condition. It is the most common inherited ataxia and is caused by a **GAA trinucleotide repeat expansion** in the *FXN* gene on chromosome 9, which encodes the protein **frataxin**. This leads to mitochondrial iron overload and oxidative damage, primarily affecting the spinocerebellar tracts, dorsal columns, and pyramidal tracts [1]. **2. Analysis of Incorrect Options:** * **Neurofibromatosis (Type 1 and 2):** Both are classic examples of **Autosomal Dominant (AD)** inheritance. NF1 is linked to Chromosome 17, and NF2 to Chromosome 22. * **Marfan’s Syndrome:** This is an **AD** connective tissue disorder caused by mutations in the *FBN1* gene (encoding Fibrillin-1) on Chromosome 15. * **Bloom Syndrome:** While the question asks for "neurological conditions," Bloom syndrome is primarily a chromosomal instability disorder. However, it is **Autosomal Recessive**, making it technically a correct answer alongside Friedreich's ataxia. *Note: In standard NEET-PG patterns, if two options are AR, Friedreich's ataxia is the "more" neurological choice.* **3. High-Yield Clinical Pearls for NEET-PG:** * **Friedreich’s Ataxia Triad:** Progressive ataxia, HOCM (Hypertrophic Obstructive Cardiomyopathy), and Diabetes Mellitus. Skeletal deformities like **Pes Cavus** and Kyphoscoliosis are common. * **Trinucleotide Repeat Mnemonic:** "GAA" for Friedreich’s Ataxia (**G**ait **A**taxia **A**lways). * **Most AD conditions** involve structural protein defects (e.g., Marfan, NF, Achondroplasia). * **Most AR conditions** involve enzyme deficiencies or metabolic pathways [2] (e.g., Wilson’s disease, Hemochromatosis, FA).

Q: Mental retardation is NOT a feature of which of the following mucopolysaccharidoses?

Sanfilippo syndrome (MPS III). The correct answer is **D. Morquio syndrome (MPS IV)**. (Note: The provided key in the prompt incorrectly marks Sanfilippo; however, clinically and for NEET-PG, Morquio is the classic MPS characterized by **normal intelligence**). **1. Why Morquio Syndrome (MPS IV) is the correct answer:** In Mucopolysaccharisoses (MPS), mental retardation occurs when there is an accumulation of heparan sulfate in the CNS. Morquio syndrome is caused by a deficiency of *Galactose-6-sulfatase* (Type A) or *Beta-galactosidase* (Type B), leading to the accumulation of **Keratan sulfate** [1]. Since Keratan sulfate is not a primary component of the brain, patients with Morquio syndrome typically have **normal intelligence**. They are characterized by severe skeletal dysplasia (spondyloepiphyseal dysplasia) and ligamentous laxity. **2. Why the other options are incorrect:** * **Hurler Syndrome (MPS I):** This is the most severe form. It involves the accumulation of dermatan and heparan sulfate, leading to progressive developmental delay and significant cognitive impairment [1]. * **Hunter Syndrome (MPS II):** This is X-linked recessive. Like Hurler, it involves heparan sulfate accumulation, leading to mental retardation [1]. * **Sanfilippo Syndrome (MPS III):** This syndrome is unique because it presents with **severe CNS involvement** and behavioral disturbances, while the physical (somatic) features are relatively mild. Mental retardation is a hallmark feature [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Normal Intelligence:** Morquio (MPS IV) and Scheie Syndrome (MPS IS) [1]. * **No Corneal Clouding:** Hunter Syndrome (MPS II) – "The Hunter needs clear eyes to see the target." * **X-linked Recessive:** Hunter Syndrome (All other MPS are Autosomal Recessive). * **Diagnosis:** Initial screening via urinary GAGs; confirmed by enzyme assay or genetic testing.

Q: Duchenne's muscular dystrophy is inherited in which pattern?

X-linked recessive. **Explanation:** **Duchenne Muscular Dystrophy (DMD)** is caused by a mutation in the **DMD gene** located on the short arm of the **X chromosome (Xp21)**. This gene encodes for **dystrophin**, a critical protein that links the cytoskeleton of a muscle fiber to the surrounding extracellular matrix. 1. **Why X-linked Recessive (Correct):** DMD follows an X-linked recessive pattern because the gene is located on the X chromosome [1]. Since males have only one X chromosome (XY), a single mutated copy results in the disease. Females (XX) are typically asymptomatic carriers because their second, healthy X chromosome produces sufficient dystrophin. 2. **Why other options are incorrect:** * **X-linked Dominant:** In this pattern, both males and females would be affected if they carry just one copy of the mutation (e.g., Alport Syndrome). In DMD, females are generally spared from severe clinical symptoms. * **Autosomal Dominant/Recessive:** These involve mutations on non-sex chromosomes (1-22). DMD is specifically linked to the sex-determining X chromosome. **High-Yield Clinical Pearls for NEET-PG:** * **The Gene:** The DMD gene is the **largest known human gene**, making it highly susceptible to spontaneous mutations (30% of cases are *de novo*). * **Clinical Signs:** Look for **Gower’s sign** (using hands to "climb up" the legs to stand) and **pseudohypertrophy of the calves** (fatty replacement of muscle). * **Diagnosis:** Initial screen shows highly elevated **Creatine Kinase (CK)** levels. Gold standard is **Genetic Testing** (MLPA); Muscle biopsy shows absent dystrophin. * **Becker Muscular Dystrophy (BMD):** Also X-linked recessive but milder, caused by *in-frame* mutations resulting in truncated (partially functional) dystrophin.

Q: A 35-year-old nonsmoking male has been diagnosed with emphysema. His father died of emphysema at age 30, but he smoked. His father also had cirrhosis and recurrent pancreatitis but did not drink alcohol. Which one of the following inheritance patterns typifies this disease process?

Codominant. The clinical presentation of early-onset emphysema in a non-smoker, combined with a family history of cirrhosis and pancreatitis, is classic for **Alpha-1 Antitrypsin (AAT) Deficiency**. **Why Codominant is Correct:** The inheritance of AAT deficiency is characterized by **codominance**. The *SERPINA1* gene has several alleles (M, S, and Z). In a codominant pattern, both alleles in a heterozygote are expressed equally, contributing to the overall phenotype. * **PiMM:** Normal levels of AAT. * **PiMZ:** Heterozygous; intermediate levels (increased risk if smoking). * **PiZZ:** Homozygous; severely low levels, leading to panacinar emphysema and liver cirrhosis (due to misfolding and accumulation of the protein in hepatocytes) [2]. **Why Incorrect Options are Wrong:** * **Autosomal Dominant:** In AD, one mutant allele masks the normal one. Here, the normal allele (M) still produces functional protein, so the phenotype depends on the specific combination of both alleles [1]. * **Incomplete Dominance:** This would imply a "blending" of traits where the phenotype is an intermediate between the two parents. In AAT deficiency, both gene products are distinctly present and measurable. * **Autosomal Recessive:** While the *disease* often manifests when two abnormal alleles are present (like ZZ), the *inheritance pattern* of the alleles themselves is codominant because both alleles contribute to the serum protein level. **High-Yield Clinical Pearls for NEET-PG:** * **Pathology:** Emphysema in AAT deficiency is **Panacinar** (lower lobes), whereas smoking-related emphysema is **Centriacinar** (upper lobes). * **Liver Involvement:** PAS-positive, diastase-resistant globules in hepatocytes are pathognomonic [1]. * **Diagnosis:** Initial screening is via serum AAT levels; gold standard is phenotyping (isoelectric focusing). * **Associated Condition:** Panniculitis (necrotizing skin lesions) is a rare but high-yield association.

Q: Adult Polycystic kidney disease is inherited by which mode?

Autosomal dominant. **Autosomal Dominant Polycystic Kidney Disease (ADPKD)** is the most common hereditary kidney disease [1]. It is inherited in an **Autosomal Dominant** pattern, meaning a single copy of the mutated gene from one parent is sufficient to cause the disease [1]. * **Why Option A is correct:** ADPKD is primarily caused by mutations in the **PKD1** gene (85% of cases, located on Chromosome 16) or the **PKD2** gene (15% of cases, located on Chromosome 4) [1]. It typically presents in the 3rd to 5th decade of life with bilateral renal cysts, hypertension, and hematuria [1]. * **Why Options B, C, and D are incorrect:** * **Autosomal Recessive (ARPKD):** This is a distinct, rarer entity caused by mutations in the *PKHD1* gene. It typically presents in infancy or childhood and is associated with congenital hepatic fibrosis. * **X-linked/Mitochondrial:** These modes of inheritance are not associated with the classic presentation of polycystic kidney disease. **High-Yield Clinical Pearls for NEET-PG:** 1. **Extra-renal manifestations:** The most common is **Liver cysts**. The most life-threatening is **Berry Aneurysms** (Circle of Willis), which can lead to subarachnoid hemorrhage. Other features include mitral valve prolapse and diverticulosis. 2. **Diagnosis:** Ultrasonography is the primary screening tool. Diagnosis is based on the number of cysts relative to the patient's age (Ravine criteria). 3. **Prognosis:** PKD1 mutations progress to End-Stage Renal Disease (ESRD) earlier (mean age ~54) compared to PKD2 (mean age ~74) [1]. 4. **Treatment:** Tolvaptan (a V2-receptor antagonist) is used to slow the progression of cyst growth and renal decline.

Q: Which of the following is NOT a common tumor associated with neurofibromatosis?

Retinoblastoma. **Explanation:** **Neurofibromatosis (NF)** is a group of autosomal dominant neurocutaneous syndromes (phakomatoses) characterized by a high predisposition to tumors of the central and peripheral nervous systems. **Why Retinoblastoma is the Correct Answer:** Retinoblastoma is caused by a mutation in the **RB1 gene** on chromosome 13. It is not associated with Neurofibromatosis Type 1 (NF1) or Type 2 (NF2). While NF1 is associated with ocular findings like **Lisch nodules** and **Optic Nerve Gliomas**, it does not increase the risk for retinoblastoma. **Analysis of Incorrect Options:** * **A. Gliomas:** These are highly characteristic of **NF1**. Specifically, **Optic Pathway Gliomas** (pilocytic astrocytomas) occur in up to 15% of NF1 patients. * **C. Schwannomas:** These are the hallmark of **NF2**. The classic presentation is **bilateral vestibular schwannomas** (acoustic neuromas) [1]. NF2 is often remembered by the mnemonic "MISME" (Multiple Inherited Schwannomas, Meningiomas, and Ependymomas). * **D. Meningiomas:** These are common intracranial tumors associated with **NF2**. Patients with NF2 often develop multiple meningiomas at a younger age than the general population. **High-Yield Clinical Pearls for NEET-PG:** * **NF1 (von Recklinghausen Disease):** Chromosome **17** (Protein: Neurofibromin). Key features: Café-au-lait spots, Lisch nodules (iris hamartomas), Axillary freckling (Crowe sign), and Neurofibromas. * **NF2:** Chromosome **22** (Protein: Merlin/Schwannomin). Key features: Bilateral acoustic neuromas [1], cataracts (juvenile posterior subcapsular lenticular opacities), and meningiomas. * **Rule of 2s for NF2:** Chromosome **22**, Bilateral (2) Eighth (2x4) nerve tumors.

Q: Complications of Wilson's disease include all except?

Peripheral neuropathy. Wilson’s Disease (Hepatolenticular degeneration) is an autosomal recessive disorder caused by mutations in the **ATP7B gene**, leading to impaired biliary copper excretion and systemic copper accumulation. **Why Peripheral Neuropathy is the correct answer:** While Wilson’s disease causes significant neurological damage, it primarily affects the **Central Nervous System (CNS)**, specifically the basal ganglia [1]. **Peripheral neuropathy is not a feature** of Wilson’s disease. In fact, if a patient with Wilson’s disease develops peripheral neuropathy, it is usually an adverse effect of treatment with **D-penicillamine** (which can cause Vitamin B6 deficiency). **Analysis of Incorrect Options:** * **Fanconi Syndrome:** Excess copper is toxic to the renal proximal convoluted tubules, leading to Type 2 Renal Tubular Acidosis (Fanconi syndrome), characterized by glucosuria, aminoaciduria, and phosphaturia [1]. * **Ataxia:** Copper deposition in the cerebellum and its pathways leads to cerebellar signs, including ataxia, dysarthria, and coordination deficits [1]. * **Hemolytic Anemia:** Sudden release of free copper into the bloodstream from necrotic hepatocytes causes oxidative stress to RBCs (Coombs-negative hemolytic anemia), often seen during a "Wilsonian crisis" [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Kayser-Fleischer (KF) Rings:** Copper deposition in the **Descemet’s membrane** of the cornea (best seen on slit-lamp exam). * **Diagnosis:** Low serum Ceruloplasmin (<20 mg/dL), increased 24-hour urinary copper excretion, and "Giant Panda" sign on MRI Brain. * **Treatment:** Chelators like **Trientine** (preferred) or D-penicillamine; Zinc is used for maintenance as it inhibits intestinal copper absorption.

Q: Which one of the following is an autosomal dominant type of genetic disorder?

Tuberous sclerosis. **Explanation:** **Tuberous Sclerosis (Option D)** is the correct answer. It is an **autosomal dominant (AD)** neurocutaneous syndrome caused by mutations in the *TSC1* (Hamartin) or *TSC2* (Tuberin) genes. In AD disorders, a single copy of the mutant gene is sufficient to cause the disease, typically manifesting in every generation. **Analysis of Incorrect Options:** * **Color Blindness (Option A) and Hemophilia (Option B):** These are classic examples of **X-linked recessive (XLR)** disorders. They primarily affect males, while females are typically asymptomatic carriers. * **Phenylketonuria (Option C):** This is an **autosomal recessive (AR)** metabolic disorder. It requires two copies of the defective gene (one from each parent) for the disease to manifest. Most enzyme deficiencies, like PKU, follow an AR inheritance pattern. **Clinical Pearls for NEET-PG:** * **Tuberous Sclerosis Triad (Vogt’s Triad):** Adenoma sebaceum (facial angiofibromas), seizures, and mental retardation (seen in only ~30% of cases). * **High-Yield Features:** Ash-leaf spots (hypopigmented macules - earliest sign), Shagreen patches, subependymal nodules (candle-guttering appearance), and Cardiac Rhabdomyomas. * **Mnemonic for AD Disorders:** "Very Powerful DOMINANT" – **V**on Willebrand/VHL, **P**olycystic Kidney (ADPKD), **D**ystrophia Myotonica, **O**steogenesis Imperfecta, **M**arfan, **I**ntermittent Porphyria, **N**eurofibromatosis, **A**chondroplasia, **N**oonan, **T**uberous Sclerosis.

Question 1

Which of the following statements about Hemochromatosis is true?

Accepted Answer

Inherited as an autosomal recessive disorder

Answer

Phlebotomy is curative

Answer

More common in females

Answer

Shows complete penetrance

Question 2

Which one of the following neurological conditions is not inherited in an autosomal dominant pattern?

Accepted Answer

Friedreich's ataxia

Answer

Neurofibromatosis

Answer

Marfan's syndrome

Answer

Bloom syndrome

Question 3

Mental retardation is NOT a feature of which of the following mucopolysaccharidoses?

Accepted Answer

Sanfilippo syndrome (MPS III)

Answer

Hurler syndrome (MPS I)

Answer

Hunter syndrome (MPS II)

Answer

Morquio syndrome (MPS IV)

Question 4

Duchenne's muscular dystrophy is inherited in which pattern?

Accepted Answer

X-linked recessive

Answer

X-linked dominant

Answer

Autosomal dominant

Answer

Autosomal recessive

Question 5

A 35-year-old nonsmoking male has been diagnosed with emphysema. His father died of emphysema at age 30, but he smoked. His father also had cirrhosis and recurrent pancreatitis but did not drink alcohol. Which one of the following inheritance patterns typifies this disease process?

Accepted Answer

Codominant

Answer

Autosomal dominant

Answer

Incomplete dominance

Answer

Autosomal recessive

Question 6

Adult Polycystic kidney disease is inherited by which mode?

Accepted Answer

Autosomal dominant

Answer

Autosomal recessive

Answer

X linked

Answer

Mitochondrial

Question 7

Which of the following is NOT a common tumor associated with neurofibromatosis?

Accepted Answer

Retinoblastoma

Answer

Gliomas

Answer

Schwannomas

Answer

Meningiomas

Question 8

Complications of Wilson's disease include all except?

Accepted Answer

Peripheral neuropathy

Answer

Fanconi syndrome

Answer

Ataxia

Answer

Hemolytic anemia

Question 9

Which one of the following is an autosomal dominant type of genetic disorder?

Accepted Answer

Tuberous sclerosis

Answer

Color blindness

Answer

Hemophilia

Answer

Phenylketonuria

Question 10

What is the most common sign in mitochondrial inheritance diseases?

Accepted Answer

External ophthalmoplegia

Answer

Ataxia

Answer

Psychosis

Answer

Neurogenic weakness

Genetics and Disease — MCQs

Genetics and Disease — MCQs

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